Gas adsorption articles or elements are used in many industries to remove airborne contaminants to protect people, the environment, and often, a critical manufacturing process or the products that are manufactured by the process. A specific example of an application for gas adsorption articles is the semiconductor industry where products are manufactured in an ultra-clean environment, commonly known in the industry as a “clean room”. Gas adsorption articles are also used in many non-industrial applications. For example, gas adsorption articles are often present in air movement systems in both commercial and residential buildings, for providing the inhabitants with cleaner breathing air.
Typical airborne contaminants include basic contaminants, such as ammonia, organic amines, and N-methyl-2-pyrrolidone, acidic contaminants, such as hydrogen sulfide, hydrogen chloride, or sulfur dioxide, and general organic material contaminants, often referred to as VOCs (volatile organic compounds) such as reactive monomer or unreactive solvent. Silica containing reactive and unreactive materials, such as silanes, siloxanes, silanols, and silazanes can be particularly detrimental contaminants for some applications. Additionally, may toxic industrial chemicals and chemical warfare agents must be removed from breathing air.
The dirty or contaminated air is often drawn through a granular adsorption bed assembly or a packed bed assembly. Such beds have a frame and an adsorption medium, such as activated carbon, retained within the frame. The adsorption medium adsorbs or chemically reacts with the gaseous contaminants from the airflow and allows clean air to be returned to the environment. The removal efficiency is critical in order to adequately protect the processes and the products.
The removal efficiency and capacity of the gaseous adsorption bed is dependent upon a number of factors, such as the air velocity through the adsorption bed, the depth of the bed, the type and amount of the adsorption medium being used, and the activity level and rate of adsorption of the adsorption medium. It is also important that for the efficiency to be increased or maximized, any air leaking through voids between the tightly packed adsorption bed granules and the frame should be reduced to the point of being eliminated. Examples of granular adsorption beds include those taught is U.S. Pat. No. 5,290,245 (Osendorf et al.), U.S. Pat. No. 5,964,927 (Graham et al.) and U.S. Pat. No. 6,113,674 (Graham et al.). These tightly packed adsorption beds result in a torturous path for air flowing through the bed.
However, as a result of the tightly packed beds, a significant pressure loss is incurred. Current solutions for minimizing pressure loss include decreasing air velocity through the bed by increased bed area. This can be done by an increase in bed size, forming the beds into V's, or pleating. Unfortunately, these methods do not adequately address the pressure loss issue, however, and can create an additional problem of non-uniform flow velocities exiting the bed.
Although the above identified adsorption beds are sufficient in some applications, what is needed is an alternate to a bed that can effectively remove contaminants such as acids, bases, or other organic materials, while minimizing pressure loss and providing uniform flow velocities exiting the filter.